For the radio-control of tower cranes, such as known for example from the European patent EP 1149796 A2 in the name of the Applicant, there are receiving or receiving and transmitting antennas for control signals. These antennas are either fixed antennas or detachable antennas.
When they are fixed, the radio-control antennas are directly fired to a point in the framework of the crane, or they are incorporated with a receiver or transceiver unit for control signals, this unit itself being fixed to the crane. The fixed antennas thus have a unique and non-modifiable position.
When they are detachable, the radio-control antennas are generally fixed:                either to a receiver or transceiver unit for control signals, which can itself be fixed to the crane at various locations specially provided for this purpose or not;        or on a magnetic or non-magnetic mount, with a sufficient length of transmission cable or with detachable cable extensions, it being possible to position the mount on the crane at various locations specially provided for this purpose or not.        
Radio-control is always interfered with by the metal obstacles located between the transmitter and the receiver of the control signals, these obstacles reducing the range of the radio control and creating echoes. Furthermore, the quality of the transmission of the control signals is greatly affected by the length of cable which connects the antenna to the receiver, by the connections associated with the cable extensions and by the quality of the electrical ground between the antenna and its support, if the antenna is detachable.
More particularly, systems with a fixed antenna or fixed antennas, having a unique position, are subjected to metal obstacles and principally to the framework of the crane itself, especially during its rotation.
Systems with a detachable antenna or detachable antennas are subjected to even more diverse factors:                difficulty with cable passages;        long transmission cable length, which must be provided for the most distant position of the antenna;        interference due to the poor quality of the electrical connections, in the case of the use of cable extensions;        frequent electrical ground continuity faults;        risk of damage to the transmission cable, whilst the crane is working, for example due to projections, shocks and climatic conditions.        